Actuating device of this class are used, for example, but by no means exclusively, for manually selecting gears or for preselecting gears in speed-change gears of motor vehicles.
In an increasing number of motor vehicle models, gear preselection or the control of the operating state of the vehicle transmission is carried out now by means of electrical or electronic signal transmission. However, the electrical or electronic actuation of technical systems or transmissions, which makes do without a mechanical connection, inevitably brings with it a number of peculiarities. Thus, contrary to operation by means of the prior-art mechanical actuating device, the operator or driver has, in general, no feedback whatsoever on the circumstance that his operating wish may be possibly inadmissible.
To avoid errors in operation in certain situations, for example, to signal to the driver of a motor vehicle certain states of the vehicle or disturbances (e.g., failure of the communication between the shifting mechanism and the transmission), actuating device are often equipped with locking systems, which do not allow certain motions of the actuating element any longer when certain boundary conditions are present.
For example, the so-called keylock system of an actuating device for an automatic speed-change gear, which is known from the area of motor vehicles, leads to locking of the actuating element or the selector lever in position “P” (parking brake). It shall thus be prevented, in particular, that the selector lever is moved into one of the gears before starting up the engine, whereby the vehicle could start moving in an undesired manner already when the engine is started.
Another example of the use of a locking means is the P/N lock in an automatic vehicle transmission, which ensures that shifting from the shift positions “P” (parking brake) and “N” (neutral) is possible only when the brake is pressed. This likewise serves the purpose of preventing the vehicle from starting to move in an uncontrolled manner at the moment at which a gear is engaged.
Electromechanical actuators are frequently used to embody such locking functions in the actuating device with electrical or electronic signal transmission, which can be encountered increasingly frequently and which make do without any mechanical connection whatsoever between the actuating element and the system being controlled therewith or even without a mechanical connection to the locking means, e.g., a keylock or P/N lock.
In other words, this means that the situation-dependent locking of the actuating element does not take place via linkages or cables any longer, but rather only electric or electronic signals are transmitted to the actuating device. These are then converted in the actuating device and used to actuate the corresponding electrical actuators of the locking means. Electromagnetically actuated armatures are often used as actuators.
Based on the large number of locking mimics, especially in shift-by-wire speed-change mechanisms, in which, moreover, often only a situation-dependent restriction of the mobility of the gearshift lever is provided, relatively complex locking systems are frequently necessary according to the state of the art in the prior-art actuating device. The control or locking is performed in the existing locking systems mostly with the use of electromagnets, which move an armature each as a function of the flow of current. However, the armature has only two possible positions, which correspond to the two states “energized” or “non-energized.”
In other words, this means, however, that only two discrete locked states can be established in this manner with an actuator, for example, “locked” or “unlocked.” However, from this arises the need, in the increasingly complex locking systems, which are used, for example, in the actuating device of shift-by-wire transmissions, to provide an increasing number of electromagnetic actuators, which have two shift positions each.
However, this is disadvantageous because the space to be made available for this plurality of actuators is not readily available. Furthermore, such electromagnetic actuators have a rather substantial weight because of the copper windings present in them, which contributes to an undesired increase in the weight of the shifting unit. Last but not least, the plurality of separate actuators also causes an increase in the cost for the shifting unit, which is often unacceptable because of the cost pressure in the area of technical systems of motor vehicles.